#include <stdio.h>
long fact(int n);
long rfact(int n);
int main(void)
{
    int num;
    printf("This program calculates factorials.\n");
    printf("Enter a value in the range 0-12(q to quit): \n");
    while(scanf("%d", &num) == 1)
    {
        if(num < 1)
            printf("No negative numbers, please.\n");
        else if(num > 12)
            printf("Keep input under 13.\n");
        else 
        {
            printf("loop: %d factorial = %ld\n", num, fact(num));
            printf("recursion: %d factorial = %ld\n", num, rfact(num));
        }
        printf("Enter a value in the range 0-12(q to quit): \n");
    }
    printf("Bye.\n");
    return 0;
}

long fact(int n)
{
    long ans;
    for(ans = 1; n > 1; n--)
        ans *= n;
    return ans;
}

long rfact(int n)
{
    long ans;
    if(n > 0)
        ans = n * rfact(n - 1);
    else
        ans = 1;
    return ans;
}
